A semiconductor wafer is material for semiconductor devices, and there are various requirements in physical properties and compositions as well as in shape, surface roughness, surface chemical properties, defect density, etc. Therefore, surface polishing and other types of processing are performed after slicing a single crystalline ingot. Abrasion dust, contaminants, debris, etc. may be generated in various types of processing and appropriate cleaning is desired. Meanwhile, a semiconductor wafer that is shipped out as a product is desired to have a comparatively stable surface, which would not be changed in its properties even after being exposed to the general air atmosphere. Especially in consideration of transportation, a wafer in a wet state is not desirable and it is rather desirable to dry the wafer for shipment.
In recent years, quality requirements for the semiconductor wafer are high such that a single wafer type is rather preferred to a batch type, and a spin dry process is adopted, in which the semiconductor wafer is rotated at a high speed for drying after the semiconductor wafer is variously processed on the surface in a wet state.
Meanwhile, since the circumferential velocity becomes very high as the diameter of the semiconductor wafer has generally been made larger in recent years, it is concerned that the properties of the semiconductor wafer may be affected. FIG. 17 is a flowchart showing a surface processing method of a silicon wafer as an example of the semiconductor wafer. The processing is largely divided into three sections. The first one is what is herein called main processing. Then, the next is final processing, in which a wet state is converted into a dry state, and shipment processing for shipping the product follows. Processing actions of the respective steps are briefly described inside the boxes on the left-hand side of the flow. Surface states of the semiconductor wafer in the corresponding steps are briefly described inside the boxes on the right-hand side.
Specifically, first, the semiconductor wafer is processed with aqueous hydrofluoric acid or hydrogen fluoride gas to remove an oxide film on the surface (S2). Since the underlying metal silicon appears on the surface in this process, the surface is put in a water-repellent state such that the surface is not wettable and dropped water is formed in a spherical shape on the surface even when the water is put in contact (S2). The surface is then oxidized by ozone water and the surface is made hydrophilic (S4).
In this state, contaminants or the like may be left on the surface such that the oxide film on the surface is further removed by aqueous hydrofluoric acid or hydrogen fluoride gas (S110). In this process, the surface of the semiconductor wafer is changed to a water-repellent state as mentioned above (S110). Then, using ozone water again, a hydrophilic film is formed on the surface of the semiconductor wafer so as to make the surface hydrophilic (S1070). The surface of the semiconductor wafer can thereby be cleaned without leaving contaminants or impurities that were contained in the aqueous hydrofluoric acid and the like on the surface. Next, to remove the contaminants in the ozone water, cleaning by ultrapure water is performed, and the surface is hydrophilic during this process as well (S1080). Since the wafer in this state cannot be shipped as is, in most cases, the liquid on the surface of the semiconductor wafer is scattered by spin drying to dry the semiconductor wafer surface (S1090).
A method is disclosed in JP-A-2002-305175, in which a cleaning gas (for example, ozone or hydrogen fluoride) is injected on the wafer formed with a water membrane such that a small chamber is formed and much gas is dissolved in the membrane, and the wafer is cleaned by using the cleaning solution having a high solubility. Then, a dry gas (for example, IPA) is furthermore supplied to dry the water film. Also, an invention is disclosed in JP application No. 2003-59879, in which a processing solution is brought into contact with a surface of a substrate W to form a liquid film and an ozone gas at a higher temperature than that of the processing solution is applied to the surface such that the surface of the substrate W is processed, thereby increasing a reaction rate of the substrate surface processing by ozone.